Behavioral inhibition (BI) is characterized by a disposition to withdraw in the presence of strangers and results in decreased social interaction and increased risk for later anxiety and depression. BI is also associated with inflammation-mediated diseases. In previous work, we studied animals that showed BI (including decreased emotionality, increased vigilance) during infancy, and found that, as yearlings, animals showed decreased sociability and increased anxiety behaviors. Inhibited yearlings also showed altered gene expression of the inflammatory cytokine IL-12. To understand the continuity of immune function and BI into adulthood, we assessed 1) concentrations of the inflammatory cytokine IL-6 in a subset of animals previously tested as infants and yearlings (age=3.36 years; n=13; 8-inhibited); 2) social behavior of previously tested animals (age=4.30; n=30; 13-inhibited) in their outdoor field corrals; and 3) gene expression for IL-12 in a new subset of adult animals (age=4.59; n=6; 3-inhibited) identified as inhibited (or not) as infants. We found continuity of BI into adulthood: the amount of time animals spent non-social as yearlings predicted non-social duration as adults (r=.461; p=.005). Immune function showed continuity as well: inhibited-animals showed decreased IL-6 production (F=6.102; p=.022) and alterations in IL-12 gene expression (F=7.161; p=.016). Continuity of BI and associated immune function into adulthood may contribute to the understanding of the role that temperament can play in health.